Re: filecache/swapcache questions [RFC] [RFT] [PATCH] kanoj-mm12-2.3.8

[kanoj@google.engr.sgi.com (Kanoj Sarcar)]

> 
> i'm already working on a patch that will allow kswapd to grab the mmap_sem
> for the task that is about to be swapped.  this takes a slightly different
> approach, since i'm focusing on kswapd and not on swapoff.  essentially
> the patch does two things:

So, I would think some (if not mine) swapoff fix is still needed ...

> 
> 1)  it separates the logic of try_to_free_pages() and kswapd.  kswapd now
> does the swapping, while try_to_free_pages() only does the shrink_mmap()
> phase.
> 
> 2)  after kswapd has chosen a process to swap, it drops the kernel lock
> and grabs the mmap_sem for the thing it's about to swap.  it picks up the
> kernel lock at appropriate points lower in the code.
>

Agreed this would be a nice thing to be able to do ... 
Other than the deadlock problem, there's another issue involved, I 
think. Processes can go to sleep (inside drivers/fs for example while
mmaping/munmaping/faulting) holding their mmap_sem, so any solution 
should be able to guarantee that (at least one of) the memory free'ers 
do not go to sleep indefinitely (or for some time that is upto driver/fs
code to determine).

Kanoj
kanoj@engr.sgi.com
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